1. Technical Field
The present invention relates to an evaluation method for evaluate the optical characteristics of an optical system, an evaluation method for evaluating a projector, an evaluation device for evaluating optical characteristics, and a screen.
2. Related Art
In a conventional optical system included in an optical device such as a projector or the like, optical characteristics of an optical member such as a projection lens or the like have been measured and evaluated by using, for example, a generalized MTF (Modulation Transfer Function) measuring device.
However, since the MTF measuring device is expensive, and the measurement itself is complicated and time-consuming, the MTF measuring device has not been easily used for evaluation of optical characteristics.
Excessive time has been consumed for 100% inspection of projection lenses in a mass-production line for example.
Furthermore, not only for a single lens, but also for optical members in a state of final composition, specifically, in a state of the projection lenses finally composed, it is difficult to measure the optical characteristics thereof with precision.
In addition, an ultra short-focus projector including “Ultra Short-Focus Optical System” has recently been developed, in which a projection engine is exceptionally close to a wall (screen) and the projection distance is extremely short.
In a conventional projector, a linear optical system including only lenses has been commonly used.
However, in the ultra short-focus projector, not only lenses, but also reflection optical systems using an aspheric mirror, a free-form surface mirror, or the like, or an optical system reflecting an optical path using a planar mirror, a prism, or the like are often adopted.
The reflection optical system has an optical arrangement in which the optical path is reflected and which is substantially custom-made, compared with a conventional linear optical system.
Therefore, in the case of measuring the optical characteristics by the conventional measuring device such as an MTF measuring device or the like, a special alteration must be performed on the measuring device or a measurement object. Otherwise it is impossible to measure the optical characteristics.
Because of the above circumstances, development of a comparatively simple measurement and evaluation method is a matter requiring immediate attention.
However, as a lens performance measuring method, which is different from a conventional measurement and evaluation method which is a simple method, a “measuring method for focal distance of lens due to moiré fringes” is disclosed in Japanese Unexamined Patent Application, First Publication No. S60-247133.
In this method, two grid plates in which pitch is identical are adjacently disposed behind a lens, generating moiré fringes by causing parallel light to be incident thereonto, and the focal distance of the lens is measured based on the gradient of the moiré fringes.
In Japanese Unexamined Patent Application, First Publication No. S60-247133, though the focal distance can be very easily measured. However, this is merely a method for measuring the focal distance of lens. It is impossible to measure the basic performance of an optical system, for example, focalization, distortion, or the like.